Large modern aircraft on scheduled air routes usually fly at great heights and require a pressurised cabin to ensure the wellbeing and the comfort of passengers. In order to reduce the mechanical loading on the aircraft hull, the pressure in the cabin is significantly lower than that at ground level, representing an atmospheric air pressure of heights between 2,000 and 3,000 m. The height above sea level corresponding to a respective cabin pressure is often described as the “cabin height”.
In all operational phases, the cabin pressure is brought in each case by means of a cabin pressure regulating system to a predetermined level, which is determined after taking account of the load on the aircraft fuselage from the differential pressure between the cabin and the environment and the safety and the wellbeing of the passengers, which requires in particular an adequate supply of oxygen. In this context, it is also important to note that the pressure in the cabin is reduced during climbing in relation to the pressure on the ground and then increased again as the aircraft descends in relation to the pressure on the ground. According to the present state of the art, it is widely assumed that a constant cabin pressure rate could be the most appropriate for passenger comfort. Consequently, in modern aircraft, the cabin pressure regulation is based on a constant pressure rate for both ascending and descending.
However, it can be regularly observed in current aircraft on scheduled flights, that during both climbing and descending the pressure on passengers' eardrums or ears is in fact not constant and that the cabin pressure setting can even result in increasing discomfort for passengers.